donk_donk_donk sound as speed increases - 90 240 wag, auto

[90_240DLwag_RedBaron]

Hi- I've got a 90 240 wag, auto, 150k that runs like a top but has recently developed a rather disconcerting noise that is intermittent - though once it starts, it sticks around for a while and is consistent.

If the car is not making the noise and I am cruising, the noise usually starts after I open the throttle suddenly or otherwise horse on it. Starts with a loud "bonk" from under the car (cannot pinpoint where) that almost sounds like the noise that might come from taking a hammer to the driveshaft or the muffler (something somewhat hollow anyway). Then it continues and varies with speed - bonk, bonk, bonk, bonk - and as I slow, the bonk becomes louder and you can almost feel the car lope a little bit with each bonk. Then at idle, no bonk, then bonk bonk bonk when speeding back up. Can't really detect it once it gets past say 25 mph.

At first I figured this was the muffler whacking against the frame when torqued, but I've ruled that out. The only think I can think of is something associated with the tranny or driveshaft - possibly the u-joints assoc with the driveshaft. The noise does not go away if I slide it into neutral by the way...

Any thoughts would be appreciated, also some test I might be able to do to pinpoint the problem. Any guestimates on difficulty and cost assoc with me fixing this vs. a shop (i just had surgery and am, unfortunately, kind of gimp and will be for a few weeks i presume) would be appreciated.

Thanks a lot,
Greg

[Kmaniac in California USA]

Check the condition of the engine and transmission rubber mounts. If one or more has rotted away, your engine & trans assembly will shift to a point that the driveshaft will contact and scrape the floorpan.

Investigate a little and let us know what you find.

[Harry von Zell]

Kmaniacs right. Start with tranny mount. If it continues, check trailing arm bushings at rear suspension.

[waynej]

Check the U-joints and the carrier bearing.