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I've had my Cadi for 3, almost 4 months now, and when I first got it the engine was very quite. (Previous 2 owners, was a company, and then an employee at that same company) Given it's history I assume, it had been babied the whole time the other 2 owners had it.

I by no means baby it, and just recently started hearing this weird spindle sound. I am also hearing a knocking sound, that has kinda ofbeen there since I got it, but just recently it's gotten more noticeable.

I took it to a mechanic and he said he thinks the spindle sound is a fuel injector that's clogged up, and he recommend running fuel injector cleaner the next 2 times I fill up the tank.

For the knocking sound, I had him drive the car while I was in the passenger seat, and he said he didn't notice anything. He said he may not notice anything because he doesn't know how the car sounded when I first got it.

The knocking sound gets slightly louder, and becomes rapid when I'm getting on the gas. The only way you can hear it is with all the windows up, and the radio, and AC off. If I made a video, I don't think you would be able to hear it.

Anyways I was hoping I could get some advice to what the knocking and spindle sound may be, if it's not the fuel injector/s.

Here's a video of the spindle sound, You can hear it better 19 seconds into the video. It's not very noticeable with the covers on, so I took them all off.
 

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2006 STS 1SG & 2007 STS 1SE
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Variable Valve Timing engines are not quiet engines. My wife's 2007 V8 is noticeably noisier than my 2006 V8, despite the higher mileage on my car. This has been true for 6 years. Do you have Mobile1 5W-30 in the crankcase and check the level every time you fill the gas tank?

You can use other oils in the 4.6 STS V8, but should not use any oil that does carry the GM4718M rating, any other viscosity, or any oil additives. Engine oil is used to control the valve timing, so low oil level will cause very poor performance. Since a drain & fill requires 8 quarts, if you need to add oil & GM4718M oil is not available, you can use some other 5W-30 oil, but don't do so for oil changes. Fortunately, the award-winning OLM has a 100% safety margin, so many members change their oil once a year.

Use premium Top Tier fuel and you should need no fuel additives, either. Top Tier fuel vendors are recommended by worldwide premium car manufacturers because their fuels will keep your fuel system in top condition. Many members advocate adding Techron, but it usually isn't necessary. My wife & I have found that the reformulated 87 octane E-10 mandated in southeastern Wisconsin runs OK in our cars. Most members experiment with mid-grade but make their own decision. The STS does have very good anti-knock sense/correction and my car shows very little change in mileage, but does seem to perform best on pure gas of 89 octane or higher.
 
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