This is on a 2002 Deville. It runs good and quiet except during a warm restart. When I have the engine warmed up, then shut it off, wait six minutes and start it up again it makes quite a loud racket for a few seconds and then runs quiet again.
The noise is like a clattering mixed with a knocking. The clattering sometimes will stop while the knock continues a little longer. Usually the whole thing is over in between five and 30 seconds. The clattering part is usually only about five seconds or less.
In addition to this, to complicate it somewhat, I've had a tappet (valve follower) noise - a clicking noise that lasted a lot longer. That tappet noise is now pretty well cured. I put some Rislone in it and it has quieted down substantially.
After adding the Rislone and with the clattering still continuing, I got to thinking that maybe it was caused by dry starts. I did another oil change and put Lucas in the crankcase instead of Rislone. When I did this, the tappet clicking noise got worse and the clattering still continued so I switched it back to the oil/Rislone combination.
Then I read about air cavitation noises in the water power steering pump. I worked with that some but found the noise was not coming from the pump. I put a long screwdriver up to my ear and touched the pump and touched near the valvetrain area and it was definitely not the power steering pump; quite pronounced on both banks as far as I could tell.
It really sounds kind of like a rattling detonation noise. With that in mind I ran the tank down to almost nothing and added 93 octane last night. It was the Shell premium that has the cleaners in it. It has made no difference in the clattering though. Maybe I need to give it a little longer.
I was reading another thread here on carbon rap and that made me wonder a little bit about the knocking noise I'm hearing (distinguished from the clattering). The knocking noise lasts longer than the clattering, but then goes away (I think it stops when the oil pressure builds up).
A while back I pulled the intake manifold and the valves did have a coating of carbon on them. It didn't seem to be excessive or very thick but it was there.
Today, since putting the higher octane in I noticed something else unusual. It sounded like sleet (or small bb's) hitting a window. Sort of a crackling sound. It seemed to be coming from the intake throttle-body area. I wonder if the cleaner could be breaking up particles of carbon or something. I don't know where that much carbon would be coming from if that's what it is.
Another idea might be a broken spring. What do you think?
I have not noticed any metal in the drained oil. I did not cut the filter in two yet.
I have not totally isolated the sound source yet. I suppose it could be coming from the oil pump, but it sure sounds like it is coming from the top.
So I've ruled out power steering pump and I'm thinking maybe one of these:
Broken or overly weak valve spring(s)
Something else in the valvetrain
Carbon related noises