I was driving around today in my 1989 DL (5-speed, M47), and I noticed under acceleration, turning, or shifting gears, I get a "thumping" noise that sounds like its coming from the trunk, like lets say a [heavy] baseball rolling around and hitting the metal. I checked the trunk, its obviously not something rolling around. I'm most definitely suspecting a bad bushing of sorts, but I do not know how to pinpoint where. Online I've read that you should try wiggling the driveshaft support or trailing arm bushing. If they have any play then it needs to be replaced.

I appreciate any help, and link to cheap parts, I'm cash-strapped at the moment.

 

You are on the right track. Check the drive line: u joints, center support bearing, flex disc, etc. There should be no sloppy play or big cracks in the rubber. Parts are widely available.

 

I'll put my $5 chip on the 'center support bearing' . this bearing was completely frozen on my daughter's 240 at around 25 years and 400k miles, and the rubber 'donut' it sits in was beat to a pulp, so the driveshaft was clunking around and bucking, causing a grumbling vibration at lower speeds. This was the 2nd or 3rd time in the life of this car we've needed to replace this.

 

So I finally got the opportunity to put the car on jack stands... here are the results I came up with.

First off, I think this stabilizer bar linkage (?) could be causing some of the noise.

https://vimeo.com/80772448

Also, my rear trailing arm bushings were hard to see from the inside, even with the car on jack stands, but from the outside you can see some of the rubber starting to crack.

 

I believe that piece is called the 'thrust rod' or 'torque bar' depending on who you listen to. and yes, those certainly would make some nasty rattle clunks if they are that loose.

hmmm, my parts catalog calls it the 'support stay'.

the bushing is Volvo PN 1273622. Odd, they don't show a bushing on the back (axle) end of that support stay.