spark plug issue?

I have a '99 Corolla. Recently I've started hearing sounds from the engine area which sound like the silencer / exhaust is bust. Problem is that if it was bust then i should be hearing these sounds even when I rev the engine when in neutral. But I only hear these sounds when the car is in gear and moving. The car also seems to have lost some of its accelaration.

A friend suggested that it might be a spark plug issue. My question is that what are the symptoms of a bad spark plug and is it easily replaceable?

Thanks

I just replaced the spark plug but the problem remains. I can still hear the 'knocking' sound when i rev the engine while in gear (in motion). Any ideas?

This started happening a couple of weeks ago when I got my car fixed after a burnt up starter and starter wiring. Maybe that has got something to do with this?

I have the same problem, I think it's more the timing belt that needs to be replaced. But then again I could be wrong. The reason I'm saying this is I've replaced pretty much everything on my car but the timing belt and water pump.... so!

if you're getting an engine knock, then the timing belt is the problem. replace that and you should be good to go.

I have the same problem, I think it's more the timing belt that needs to be replaced. But then again I could be wrong. The reason I'm saying this is I've replaced pretty much everything on my car but the timing belt and water pump.... so!

I already had the timing belt replaced.. (its the really big thick belt around the left side of the engine ..right?).. but that did not fix it. I didnt get a tune-up though..only a timing belt replace..do you think that would help?

I am getting the same knocking sound. It's only when in motion. I really hear it when I make hard left turns. I thought it was an exhaust leak but no luck there. I was thinking more of the transmission but toyota has a good track record with there transmissions. My timing belt has never been changed and it's up to 90,000 miles. I was going to do it this fall. Did you find out the problem? Thanks.

That's not the timing belt. That's the "fan" belt or serpentine belt. There is no timing belt on the Corolla but instead has a timing chain, which is a good thing. :-)

If it's a knocking/clicking sound when you're turning, it's the outer CV joints. Can't remember which side is bad...if you turn left, I think it's the right side that's bad and if you turn right, it's the left. Check the CV joint boots and see if they're cracked or torn open. If they are, then it's most likely your outer CV joints have gone bad.

If it's knocking/clicking when not turning but under acceleration, it could be the inner CV joints.