I just wanted to isolate some of my problems here. Maybe they're all related, maybe they are not. Also for future reference as I see mentions of this problem on several forums. There are lots of different schools of thought, the prevailing one being the motor mount on the passenger side.

Symptoms:

In the AM when I do a cold start, my engine seems to rumble/vibrate. It goes away after 15-min or so, but you can see from my videos (the clicking is my turn signals). When I am turning left, the sounds seem to go away. When I turn right the sound is louder.


I may try to take better videos to capture the sound better as it seemed to get a little worse. I also hear "bumps/thumps" when hitting little bumps in the road.

Mazda6 Rumbling noise after cold start. Acceleration. - YouTube
Mazda6 Rumbling noise on acceleration after cold start - YouTube

Possiblities:

1. Exhaust Leak- I had an exhaust leak before. I fixed it and took it to an exhaust shop who did not see any exhaust leak.

2. Motor Mounts- I see online that Motor Mounts are often a problem with this. I took it to a tire shop to get the struts looked at, they said the bump sounds when I hit things in the road were caused by the Motor Mounts and not the struts. When I took it to a mechanic however, he said the motor mounts were weak but was not causing the sound.

3. Serpentine Belt tensioner- Mechanic took a look last week and said it was the serpentine belt tensioner. I asked to hold off until I did some research and checked the struts for the suspension. I took it back this AM and the mechanic took a test drive with me and said it was coming fromt he serpentine tensioner. He showed me why he thought it was not the motor mounts by showing me when stopped and giving it gas and putting it from reverse to drive, etc that it was ok. Going to get that tensioner replaced on Thursday. At least if it doesn't fix it, I can complain and maybe have them back up their work? ???

Any other thoughts?

 

I got the serpentine belt tensioner replaced today. Seemed to quiet it down a bit, but my engine was a bit warm and most of my problems happen on cold starts. The mechanic insisted that the sound i was hearing and the vibration was the tensioner, but on the work order afterwards they noted that the mounts were "weak" and doing some vibration. When I was doing my sharp right turn, I could hear a little noise.

I still think its the engine mount on the passenger side, I am pretty sure the rubber is cracked on it + when I brought it to get my struts looked at due to a rough ride they said my engine mounts are bad. The wishbone mount I had looked fine when I had my car up on the rack. I will probably know in the AM if the sound is back, but I think I'll get that mount replaced.

Something that I read in my research was the possibility of a heat shield rattling. That could be to the motor mount holding the engine in a position that something rests on the heat shield?

My theory is that the mounts are bad, engine in a bad position, and especially when its cold. Sound possibly from a loose heat shield as well.

 

Not the serpentine belt tensioner. Sound is there still this AM and the vibration, I'm pretty sure its the passenger side engine mount, they refunded all my money for the tensioner, which was good. Going to get that mount done.

 

I hope you had the belt changed as well.

 

yes, thanks for that. I don't know if it did anything though, I think it was their misdiagnosis. Luckily I came in there telling them I thought it was the engine mount..they said it was the tensioner, then came in a second time after I had taken it to a suspension/brakes/tire shop regarding the mounts again (and they insisted it was the tensioner making the noise again). So I got it done. I've been more careful documenting what everyone is saying (using Evernote to save everything on my car now, its really good for note taking).

 

GOOD. Pretty soon you'll have a brand new car!
I think those should have been changed anyway, if you haven't before.

 

Yes, definitely the mount. Its back to "normal", no more grumbling on startup. Mechanic said the noise was the mount bottoming out.

(note, he did tear a little of the rubber off when checking it out when I brought it in, but it was cracked but visibily looked "ok".)

 

Which engine mount was that?
Did you replace it with ones from AWR?: All Parts - Engine Mounts - Mazda6 - 2003-2004 - AWR Racing Store
How many mounts did you change?

 

top passenger engine mount. the wishbone one under the car looked fine when I had the car up.

Didn't do AWR, just did whatever the mechanic ordered. probably SHOULD have done it that way but even I was unsure if that was the problem or not and was not sure if mechanic would install a non-OEM part that I brought in. If it happens again, I'll do an AWR but i just wanted it replaced asap and didn't want to wait for ordering, shipping, etc. I just was looking at that online and it looks a lot different from the OEM part.

http://store.awrracing.com/products/...nger-Side.html

Total was $240 installed. its like night and day. going over bumps, driving around, manevering, etc is all much better.