Clunking sound

is it a noise that you hear only with acceleration and just one knock of is it noise that is constant with road speed and do you hear it when braking?

It happens only with acceleration, and only between 20 and 30 mph. If I take my foot off the gas, the noise will stop.
It does not happen while braking.

The mechanic (who is at wit's end) is thinking MAYBE it is motor or transmission mounts. He suggested it could be the drive shaft, but the sound would be coming more in the center, and back further. Presently the sound is under the driver's feet.

problem is that sounds travel and can be amplified by the cars body work, so not all sounds can be coming from where you think they may be, i would start by doing a close inspection of the drive line, looking at uni's. shaft ends and CV's, then suspension, also make sure engine and trans mounts are ok, very hard to say exactly with out a first hand inspection.

My friend, whose car this is, says the mechanic has checked all these things. He has a good reputation and refurbishes Subarus for a living. So it's a little odd to have him stumped. (She just bought the car from him and he promises to make good on it.) I just thought we might get some new ideas by putting the question up on a forum. I understand it's a difficult thing to diagnose from a distance. Thanks for taking the time to respond.

You will just have to start looking at all the drive line and suspension very carefully, if there is a problem a good mechanic should be able to locate it with out a lot of trouble, but as i mentioned , noises can travel and be amplified and this makes them tricky to locate sometimes.

OK. I'm the one paying, and I just may have the car taken to another mechanic to look it over. The problem is that the sound doesn't happen every single time. And the current mechanic is telling us we are going to have to wait until it happens all the time. My worry is that if it is serious and we wait, something that is about to break, breaks at the wrong time. He says not to worry!

Hey Jim,

Try this, open the hood and start the engine. Then with your foot firmly on the brake put the car in drive and when your foot is still on the brake pedal apply a little bit of gas to the engine to see if it jumps upward. This will let you know if the engine mounts are good.

Please let us know happens so it will help others.

Best, Ken

What?? Not only does that sound dangerous, who get's to be looking under the hood when the car lurches forward? I don't get it. Of course it will jump forward, or am I missing something? Or you mean to just see if the clunk happens? Why the hood open? I'll try it if you would explain it a little more clearly. I'm slow!
....
I do have some new information though. I walked into another mechanic's shop, to see whether I could get someone else to look at it. He's the guy I go to and something of a genius. I barely got the story out when he said he's seen this all the time with Subarus. That there are bad replacement axles being made these days. And he's had to replace replacements multiple times. He said the problem is in the CV joint, and the joint being sealed he couldn't inspect it anyway. But he seemed very confident it is that.

So now we're kind of stuck because the mechanic who sold it to us, will honor the warranty but doesn't want to work on it until the sound is chronic. We haven't presented him with this new information yet though.

Yes you don't let the car move just give it a little gas with the brake on tight and see if the engine jumps upward. This will let you know if the engine mount is broken.

OH! I'm sorry, I thought you meant see if the CAR jumps forward! You mean the engine. Interesting idea. I don't believe that was looked into. We'll try it. I'll let you know.

Sounds good let me know what you find.

Best, Ken

how did you get on with this problem?

Sorry, I haven't posted anything because nothing has developed. I described to my friend the test that Ken had described, and she refused to do it (I guess thinking she'd feel bad if she ran me over by accident). And she's been busy at school - which she commutes 40 minutes away to, and interestingly hasn't complained about the noise in the past couple of weeks. She basically is willing to follow the demand the mechanic who sold it to her, and wait until it happens more often. I'm leery of that but she says the mechanic doesn't think it is dangerous. I will post something whenever this gets resolved, but I have no idea when that will be at this point.

Sounds good, I don't want you to get ran over, I should have said for you to stand to the side and not in front of the car. my bad.

Best, Ken