Slight knocking sound at takeoff

[BOOSTR]

I recently noticed a light knocking sound when taking off from a stop in 1st gear under light acceleration. When I take off hard there is no sound. Same if I take off in 2nd gear, no sound. Its more of an annoyance than a major problem right now. But I would like to fix it before it becomes a problem. Anyone else have this situation? I have 47K+ miles.

 

[sickspeed94]

describe the knocking please? also does it every happen at idle (while revving or not)? deceleration? does it go up and down with RPM? etc.

 

[Puckpimp71]

I think something's loose under your hood. Check the EM heatsheild and see if anything else could be rattling.

 

[BOOSTR]

The sound occurs only if I feather the throttle at take off in 1st gear. Mashing the throttle or reving before engaging the clutch does not produce the noise. Its just strange that it only happens under light throttle and only in 1st gear. I am thinking its the motor mounts allowing my upper hard pipe to bounce off the master cylinder perhaps. Its not an engine knock or anything like that. Its time to get the floor jack and block of wood so I can check the mounts.

 

[MSP #167]

it is probably doing it all the time you just can't hear it because you are revving the engine up.

 

[msp35]

I'm betting on a loose heatshield. Mine will rattle up to 2900 rpms if I slowly roll into the throttle. But, not if I just hammer it.

 

[BOOSTR]

Its not a heatshield rattle nor does it do it all of the time. Oh well, I'll figure it out later and report back what I find. My money is on the rear motor mount. Guess no one else has this situation.

 

[Stormtrooper77]

Could be the clutch itself.

 

[MazdaSpeedTurbo]

i had this situation it stopped doing it after i changed the oil..

 

[mspdfreak]

Do you have hardpipes? My top pipe was rubbing against the brake mater cylinder on light take-off in 1st gear.

 

[MazdaSpeedTurbo]

i have fmic as you can see in sig

 

[BOOSTR]

All motor mounts are intact. I adjusted the hardpipe, added some kartboy exhaust hangers, and gave it a SEAFOAM treatment and cleaned the throttlebody. I'll see what happens when I drive it tomorrow. It will definitely accelerate smoother.

(mspblack)

 

[BOOSTR]

Problem solved. It was either the hardpipe or the exhaust piping. Not sure which, but I am glad its fixed. Now I have to swap the kartboys out as I put the 12mm up front and the 10mm in the rear. Neither one was as wide as the oem rear hangers, but they keep everything in place and virtually eliminate any vibration.