My alternator belt is really noisy...it's hard to describe. Not a squeal like a loose AC belt it's more like a squeakey knocky sound. It's been getting worse for a few months...it used to go away once the engine warmed up but now it bad all the time. The belt has about 15k miles and the tension feels about right - a little play between both pulleys. I have not tried to adjust it yet. Can't remember the brand of the belt but it has a ribbed surface (i.e. not smooth belt against the pulleys). Out of desperation and because I had a can in the garage, I sprayed it with CRC Belt Conditioner and holy crap the noise got much louder (same weird noise just louder). Any recommendations for quieting it down short of replacing the belt?
TIA,
Mike

Check alternator mounting and bearings, since you're hearing unusual noises.

What brand is the belt?

I don't remember the brand of belt. It's been on since I rebuilt the motor 6 years ago. If I do get a replacement, is there a recommendation?

I've had good luck with both Gates XL belt you can buy from Oreilly's, as well as the Contitech belt.

BTW, back when I used to Daily Drive a 4 cylinder, the longest time I could get on a belt before it started cracking, and the belt surface polished itself (which causes the squeeking) was maybe 2 years..

Loosen the belt tension and see if the alt moves around. I chased a squeek/rattle for a long time. It was a loose bracket. I couldn't maintain the proper belt tension either. The 2 nuts that retain the bracket to the case were a real hassle to access. Steve pratel went thru a number of brackets on his 912E. A current thread of his shows what's involved when dealing with the bracket.

I have your old 4 cylinder engine out while the car is being repainted and although the belt looked great I replaced it with a Gates belt.

I threw the original belt in my emergency spares kit.

Thanks. I'll try a new belt and check the brackets bearings etc while I have it opened up. I'm currently dealing with a plugged Weber idle circuit on #3 that feel like theres a chunk of rubber in the idle jet hole. It's definitely not the o ring but when I try to install the jet something squishy in the hole keeps pushing it out. I can remove the jet and the mixture screw while running and it makes no difference. #3 CHT doesn't move when I start the engine. I tried carb cleaner but no luck. Looks like it's carb rebuild time.

Use an inspection mirror and a flashlight to look inside where the idle jet goes and see if you can see an obstruction. If you remove the idle jet and hold it up to the light, look at it with a magnifying glass (it's a very small hole) to see if you can see through the hole. If it is blocked, use compressed air to clear it. If that doesn't work, use a small strand of copper wire to clear what ever is in there. But then again, it might just be carb re-build time. If you re-build the carbs, make sure you use one or more good fuel filters.

There's something jammed in there that I can't remove with on the car. Time for a rebuild and install Jet Doctor to reduce idle jet clogging issues

Got it running again after rebuilding the carbs. My neighbor was helping me adjust them and was certain the belt noise was an alternator bearing. Given he's a retired machinist (the old fashioned type before CNC) and pretty good diagnosing noises I decided it was time to get to the bottom of it. I removed the belt and it looked glazed but the alternator mounts were tight and the bearings felt perfect. So Bob, who can fix damn near anything that doesn't have a computer attached, asked for some sandpaper and went to work removing the glaze. While he was doing that I cleaned the sticky belt conditioner from the fan and alternator grooves. That completely fixed the problem. I'll order a spare belt but for now I'm driving the hell out of it before it gets hot in Phoenix.

Not long ago a 914 friend came by with an unusual slapping/ knocking noise.
It turned out to be an alternator belt with a large piece flapping loose from it's outer surface. Cut the flap off to confirm then replaced the belt.