Help Cadillac Tech can't find annoying cabin noise

[JTWEX]

My 2002 Cadillac STS is making the most annoying cabin noise & the Cadillac service tech hasn't been able to locate the culprit. It sounds like an electrical arch emanating somewhere between just beneath the steering column all the way to beneath the foot pedals. If you lay on your back/side beneath the steering column & try to isolate you can only guess as to the exact location as the sound echos in that tiny area. The vehicle must be driven a while before the sound starts & it gets worse the longer you drive it. It sounds like a leaf stuck in a motor (like when we put cards in our bike tires as kids) & each revolution of the motor produces an arching sound (or a mild bug zapper sound). The sound persists even when the main fan/air/heat is turned off; though the tech replaced the entire blower assembly as an educated guess. Cadillac had asked that I bring it in 'running hot' with the sound as loud as it gets so they could quickly remove part of the under-dash for a hands-on evaluation; this got me nowhere as they didn't immediately inspect the vehicle as promised. They waited until the next morning to start their work & by this time the noise was gone. After four days of "failure to diagnose" they asked me to pick up the vehicle & re-schedule another appointment next week when the head mechanic gets back. The tech heard the noise when I brought it in 'hot' but hasn't been able to eyeball the problem once he gets into the cars innards.

Does anyone have any idea what motor/relay/?? (located below the steering column through the floor pedal) might be causing the most annoying noise a cars innards can make????

[submariner409]

Stick your ear next to the little (1") square grille just left of the steering column. That's the air intake for the climate control cabin air temp sensor, which uses a small muffin fan 24/7/365 to pull air in through the grille and over a thermistor/circuit board before dumping it out under the dash.

If that's the culprit, pull the grille off with a paperclip hook, being careful not to hook the small black thermistor just inside the opening. Start the car and blow out the area and tunnel with computer cleaner compressed air. If that doesn't work, you'll have to go to www.rockauto.com and drill down to your car, heating and a/c, cabin air temp sensor, and get a new unit, about $25.

Open the driver's door, stick your finger in the grommet/hole for the vent to the window air discharge (black grommet) and pull the whole end panel off the side of the dash. Take a hard look inside and pull the plastic air tube. Now, look for a small hex head bolt straight in, about 8". Loosen it and, using a set of clamp fingers or magnetic socket, remove the bolt. Now you'll have to (many magic words) snake the sensor board, connector first, sideways out of the dash. A computer geek would replace just the muffin fan. (Radio Shack, 12v). Do it the easy way and get the whole board if that's your jollies.

FYI, this reply has been posted and repeated 7 times since 09-06 by 3 different members. It's all in here somewhere covering anything you ever want to know about Cadillacs and engines. Searches work wonders. IMHO.......

[Ranger]

the Cadillac service tech hasn't been able to locate the culprit.

That's surprising. Follow Subs advice or tell the tech to check the aspirator fan.

[ewill3rd]

Does the noise stop or does it go on and on while you drive?

Try changing the temperature up and down with the climate control.
Sounds like it might me either the mode door actuator (which usually quiets down after a while) or the temperature door actuator. The temp door might get worse once the cabin reaches the temp range it is usually set at. It might be grinding trying to make small adjustments up and down in a spot where the gears are worn off.
Unplugging an actuator while the noise is happening is probably your best bet for isolation.
You can familiarize yourself with their locations and just leave the hush panel off for access until you pinpoint this noise.

[JTWEX]

Ewill-Sub-Ranger,

Thank you for your fast replies & thorough responses. Let me first say that the STS is still under the original factory warranty as I purchased it new in 2004 (Something to do with the 03's having huge incentives leaving the 02 sitting). It sounds strange that I'm seeking advise here when I still have unlimited free GM service but this vehicle has now been in the shop for a combined 7 days over three separate appointments with no success. My dealer means well but they are leaving the vehicle sit too long (overnight) before doing their 'eyeballing' even though I bring the vehicle in sounding like a bug zapper. The vehicle needs about a 30 minute drive before it starts zapping & for some reason turning the blower on full tends to expedite the noise. Once the noise starts, you can turn off the climate control & it will still hum a bug zapper theme. Having said this, the longer you drive it the louder it gets with a two hour drive being about the worst it can get. The tech (after switching out the blower) examined the air take (3/4 in-sq) & the sound doesn't appear to be coming from that little intake to the left of the steering wheel. It could be coming from the area by your feet somewhere near the illumination light on the drivers left foot area.

I have used your advise to repair my older Cadillac's & you people are almost always ahead of the techs that I pay for service. I plan on making a list of the 5-10 most likely causes & bring that to my next Cadillac appointment. Based on listening in a quiet garage I can narrow the noise location to within a foot of the brake pedal. The tech heard the noise & mentioned it could even be coming through the engine compartment. He wanted to start removing panels while the noise was at its loudest but letting it sit a day defeats the purpose of me bringing it in 'hot'.

Thank you again.

[Ranger]

After reading you last post, It does not sound like an aspirator fan. Other than that, I am as lost as the tech is.