I noticed my 1993 Honda Accord LX (automatic transmission, 118k original miles) is making a strange grinding or bearing noise. The low-medium volume noise happens immediately after you take your foot off the accelerator, and lasts maybe 1 second. While I can hear it well at lower idle speed, I happened to notice it occurs when the car is stationary; I can put the transmission in neutral and press & release the accelerator and hear the noise clearly. Again, the noise only happens immediately after I remove my foot from the accelerator peddle.

Car is in great shape considering its age, and I’ve done most of the service on it myself, with exception of minor body work and timing belt. Engine & transmission oil seem clean. Operationally, car runs and shifts just fine.
I'm assuming the noise is coming from the transmission, however I wonder if vacuum can have something to do with this, as the sudden deceleration could have something to do with vacuum? Any ideas?

 

You need to get some help and try to isolate source of noise. It could be vacuum related or not.

good luck

 

Turns out the problem was the catalytic converter. It broke down inside, and the stuff inside made that brief, loud noise. Problem confirmed and replaced!

Garage that did the work thinks the damage could have been caused by the faulty ignitor I had not too long ago. Thoughts?

 

Frequent misfiring puts a lot of unburned fuel through the cat. That can overheat & plug it up.