Intermittent Knock at Highway Speeds

willysmd · Post by **willysmd** » 16 Sep 2020, 18:01

Hey Everyone,
I have a 2001 V70 2.4 na with the 5-speed M56 and 185,000 mi on the clock. In the last month it's started making an intermittent knock that sounds like it's coming from either the engine or transaxle. I only notice the sound when I'm in 5th gear between 65 and 80mph. For some reason it seems to go away in the 80's and 90's. It happens whether I'm giving it throttle or allowing it to engine brake and I haven't noticed it with the clutch depressed. I've tried driving around town in low gears revved to a similar point (3-3.5kRPM) but have not been able to replicate it. I have no idea what could be causing it so I'm hoping someone else has diagnosed a similar problem. Thanks!

willysmd · Post by **willysmd** » 02 Oct 2020, 10:57

I just had a thought on this matter I'd like to run by the knowledge base here. I get a pretty loud rattle when I reverse up hills or back up a trailer (especially backing my camper up my driveway). This leads be to believe the dual mass flywheel is not living it's best life. Could that also contribute to the clunk I hear on the highway? If so, why only at high speeds?
Thanks!

Post by **chrism** » 03 Oct 2020, 08:01

Since you only hear it at speed, maybe something is flapping in the wind. Mud flap, splash pan, front chin spoiler, ?????

Post by **darrylrobert** » 04 Oct 2020, 20:35

The upper engine mount is a popular source of knocking. I swapped mine with a poly bush and can highly recommend it. Then look at the suspension and drive shafts , I doubt its anything to do with your clutch/transmission.

IanRush · Post by **IanRush** » 05 Oct 2020, 13:13

Engine mount or axles

IanRush · Post by **IanRush** » 05 Oct 2020, 13:13

darrylrobert wrote: ↑04 Oct 2020, 20:35 The upper engine mount is a popular source of knocking. I swapped mine with a poly bush and can highly recommend it. Then look at the suspension and drive shafts , I doubt its anything to do with your clutch/transmission.

It can be transmission only when changing gears D-->P etc

willysmd · Post by **willysmd** » 09 Oct 2020, 15:48

The upper engine mount is a good idea. When I push on it there doesn't seem to be too much play or any noise. I'll try revving it with the hood open to see if it moves much. I got under the car to check for anything loose and I didn't feel anything that was off. I did locate the sound of my supposed flywheel noise. The cat heat shield completely rotted off it's rear bolts so when the clutch chatters it was causing the heat shield to rattle on the bottom of the car.

willysmd · Post by **willysmd** » 08 Mar 2021, 18:20

Well it's been 6 months and 11,000 miles since my last post. I did the upper engine mount to no avail. The knock has gotten a lot more common. It happens every day now but still just between 60-82ish. I've been paying close attention to when it happens and realized it's vehicle speed dependent rather than engine speed. It will happen in 4th or 5th gear, or coasting with the clutch in so long as the speeds are high enough. To me, this means the problem must be somewhere between the output side of the transmission and the wheel. The CV shafts feel tight but I noticed tonight that I can rotate the drivers side wheel 1 or 2 degrees before the inner joint will start to move. I replaced both of the CVs with Rock auto cheapies (Trakmotive) 50,000k ago.

Here are my questions:

Could a sloppy CV possibly only make noise when driving straight at highway speeds? There is no popping on tight turns in either direction and no noises at speeds under 60 or over 82.

What CVs do you guys recommend? I'm thinking of getting some more cheap shafts just to see if the problem goes away.

Post by **Blacklab467** » 08 Mar 2021, 19:55

I tried 2 sets of Cardone's CV axles from Rock Auto, my stock ones were worn out at 255000kms, After the Cardone's I went to the auto wreckers and got a good set of OEM GKN Lobro's. I will not run anything other than OEM CV's in these cars. Both the aftermarket ones vibrated on acceleration at around 50-70 Mph. Lesson learned, at least they're easy to change! I really don't think thats your problem though, being that it's speed and not condition related.

willysmd · Post by **willysmd** » 09 Mar 2021, 18:42

I would love to find some OEM axles for a decent price but I think my chances of finding a m56-equipped p2 in the savage yard is slim to none. I'll probably just toss another cheap axle in and hope it lasts another 50k miles. Who knows, maybe it will even take care of the knock