So I took my chances and drove the half-resurrected 240D to work tonight. All went well on the way, but as I went to go home at midnight, a very loud squealing ensued, first at about 2000 rpms and up, and later on and off at idle, too. I noticed a while ago that the AC belt felt a bit loose, but didn't squeal, so I'm guessing that's where the noise is coming from, but hard to tell. I had my mom pick me up and left the car there ... I wasn't smart enough to have my toolbox with me.
I'm going back in the morning to tighten the belt and hope that's what was making the noise. Anything else it might be? It was much colder when I left work than when I went to work, so I would think the temp maybe had something to do with the sudden onset.

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

My first guess would be the alternator belt. You went to work during daylight hours I assume, and it was dark at midnight thus putting more load on the alternator. A/C or defroster would put more load on both the A/C and alternator belts. So, I'm with you that tightening all the belts will take care of the problem.

Paul

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84 500 SEL (307,xxx miles)

x2 That kind of load with a loose belt is a definite squealer.

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1981 240D 143k 4 spd manual -SOLD

2004 VW Jetta TDI 5 speed 300k -still driven daily

SD did the same thing the other day after it's 18 month hiatus.

The alternator belts had about 1" of displacement in the middle.

Well, after about two hours in the parking lot at work, it seems to be fine. I tightened the AC belt, which was easy, and it still squealed. So I tightened the alternator belt, which was a monster job since the adjustment bolt head is stripped ... guess that's the next repair. It still sounded funny. Then I noticed the PS belt was not only loose, the pump was hanging off one bolt ... one bolt was gone and the third was loose. So, after a long drive to Pep Boys in the Jeep to get the correct bolts, I stabilized the pump and all seems A-OK. I think last time I did not use self-locking nuts, and it must have just backed out. I think it's also a queue to replace my motor mounts, because the engine shakes the heck out of everything attached to it.

It does still make a very subtle tickity noise at idle ... almost a rattling, and I can't tell where it's coming from. I don't think it's a valve because it doesn't have a particular rhythmic nature or pattern. It's very faint. Hard to tell much of anything because of the bad exhaust, which I guess could be related to the ticky sound. I'm going to do another valve adjustment, anyway, just to be safe.

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

The ticking is probably injector nailing. Very faint is normal, I believe. I've never heard of a valve making any sort of noise.

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1983 240D 3.0T 4-speed manual, now sold

1989 Subaru GL Wagon 5-speed Touring Edition

Could be ... it does quiet down at throttle so that would make sense.

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

I had a belt squeaking on Smash a few months back. It was the alternator belt alright, and I hate having to replace that belt on these cars!!
Anyway, it was just a bit loose, but what I couldn't see until I removed it was that a portion of the inside of the belt had broken/shredded off. It was tight and outta sight at certain positions of its travel. Removing it allowed me to see the extent of the damage.
I hate that alternator tensioning system!!!!
Funny, something else I just remembered. I had to of course remove the other belts to get to this one, and my power steering pump was also held on by only one screw. And it was staying tight somehow.....
Don't give up on Chase. This won't be the last hiccup.......

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John