So this just recently started happening once it started to get cold. There's a scratching yet squeaky sound that comes from the engine bay when I hit around 35 miles an hour. It stops when the engine warms up enough. This sound is loud too. If I have my window down I can hear the sound get bounced off anything I pass very clearly. The sound doesn't increase or decrease with speed it just starts squeaking at 35 and stops when I get below that again.

I have a manual 96 XJ 4.0L

does it change when you hit the clutch?

No. I could be in any gear, neutral, or have the clutch in and it doesn't change

It sounds like you have an idler pulley or alternator bearing going bad. These usually show up when the weather starts to get cold.

^that. Remove your serpentine belt and start turning the pulleys checking for noise,binding,wobble,etc.

I had a Cadillac that would spin the alternator bearing in the case until it got warm every winter Earl. Even brand new ones would do the same thing. Turns out they were using bearings which had too stiff of grease in them. But in his case here the lube is probably just getting old and hard so it doesn't want to turn until it softens up a bit and cold makes this worse as you know.

All the same brand alternator?

Hope he gets back and let's us know.

Unfortunately, yes they were the same. But for this high amp application they were the only ones who made it at the time. 76 Seville with two high amp draw fuel pumps, auto adjusting air ride electric pump and of course all the electric bells and whistles. It really did need that high amp alternator and at that time they were not that common like they are now.

I ended up parking it because of all that crap, I was constantly working on bells and whistles. Know anyone who wants a good Olds 350 engine? lol

This reminds me of a service call I had one time on an actuator at a waste water plant. The control system would pulse the actuator every few moments to slowly lower an arm down into the water to decant the top of the water. Customer said it stopped working after it got cold out.

After some head scratching and digging, turns out the manufacturer starting loading the actuators with cheap grease that would become too stiff during the winter. So the tiny pulse of power it received wasn’t enough to overcome the stiffness of the grease. If you left the power on constantly, it would eventually start to move. The solution was to wrap it heat tape. Works like a champ now.

I think this might be more common than we would think. Lubrication is a specialty science for a reason. I had another case of the same thing happen. We had a bunch of Peterbilts with the ISX Cummins. Cummins had contracted with Horton to supply their fan hubs. Same thing cheap grease, it would get so thick it wouldn't even stick to the ball bearings inside to actually coat them. So every winter they would all go bad in just a few thousand miles just like they were completely dry. After the truck went out of warranty we would rebuild these fan hubs ourselves and put in the correct bearings. Never had problem after this.

Wow. Interesting! Funny, how the devil is in the details.

You hear/read a lot about the use of high temp grease. Not enough on the use of low temp though.

$400 fan hubs! What did they save on this grease? 5 to 10 cents?

You can pull the belt and spin each pulley and hope to feel/hear which one it is. Other option is to use a stethoscope on them with the engine running. An easy DIY stethoscope is a long screwdriver, put the end of the handle against your ear and touch the tip to different parts, you'll be amazed at what you hear. If you touch an injector you can hear it clicking.

Sorry for being absent for a few days there. Based on what I read I'm gonna replace my belt (which needed it anyways) and while I'm doing that I'll check all the pulleys for noise. I'll also lube up my alternator bearing thing to see if that helps.

If it were one of those pulleys wouldn't it always be making the scratching noise even when I'm idling though?