I posted this as a reply to another problem, but it was buried and didn't fit that OP problem well. I am setting it in a separate posting as there are continuous reports from time to time about cold start noises of various kinds on XK8s and XJ8s. These are some of the common sources of the noises.

I've found numerous sources for cold start "sounds or noises" on XK8s some changing by MYs. Owners describe sounds like - Crickets, clicking, ticking, tapping, squeaking, squealing, grinding, etc. Most of these sounds can only be heard at idle and/or cold engines, with reports of the sounds going away after warmup and/or higher rpms.

When I diagnose a customer complaint I check all of these. The sources that can contribute to these sounds:

Serpentine belt (worn or cheap replacement belt, even new)
Idler pulley (dry bearing)
tensioner pulley (dry bearing)
Air compressor clutch (test by shutting off air con at cold idle)
VVTs
Bad alternator bearing
Noisy water pump (bearing - rare but often on new cheap non-OEM pumps)
Secondary tensioners going out - although more rare (old style plastic with missing slippers)

Belts usually contribute to the squeaking/squealing as the cold hard rubber belt warms up it quiets down. Some of the cheaper belts are not manufactured true and will squeak/squeal with a cadence until the belt warms up.

Crickets or clicking is almost always the air con clutch - shut off air before cold start and listen for a change in sound.

Tensioner and idler pullys can cause a grinding or squeaking sound and often fades as the little bit of grease warms up and redistributes onto the ***** and races.

 

Good post, but where are the noisy clicking normal operating injectors?
And lets not leave out the supercharged back lash rotor noise at idle which is normal up to a point.
Then there the occasional snake or cat noises on cold start

 

Good additions, the injectors are definitely an oversight on my part. Add them on the list.

 

And to pinpoint i cant recommend enough a mechanics stethoscope theyre cheap like $10-15 at sears

 

I appreciate your summary Steve, and with brutals additions too. I'll put this thread link into the FAQ section, hopefully that'll be found by the new members and the number of 'cold start noise' threads will diminish, or at least contain diagnosis and some additional troubleshooting background as to work with.

 

Did you ever figure out what the cat noise was caused by?
On a cold start today, was the first time I heard this cat noise but I have only started the car about 100 times as I just bought it. It sounded like a cat giving off a pissed off throaty growl.
I also noticed recently the car sounding like I punched the gas at start as the rpms for the first second or two were higher than usual starts.... does this point to anything that anyone knows of?
thanks for reading

 

Thanks Steve11, see if you can diagnous this one!
Unknown Knock? video by guzzisvt | Photobucket
The first video (the second video was primary timing chains, got that fixed).
It only makes the noise while in gear and goes away after heat soaking the engine. (i.e. running a short time and letting it set does the same thing as running that same amount of time)
Comes from the SC area even w/o the SC hooked up.
The dealer says it come from bottom of the engine when the car is on a lift too.

Thanks!

 

Hi Bill,
No help on the solution, but to assist, My XJ8 no supercharger sounds similar and has the same warm up solution including the heat sinking method.

 

Thanks Mark, be sure to let us know if anything ever flies apart.