Tapping loud, not a knock but had a lot of work done recently...

[lady_x_calibur]

1997 Chevy Blazer LT AWD 158,000 miles

-Replaced radiator, heater core cleaned out due to overheating problem/sludge from Dexron, also had manifold gasket replaced due to minor pressure leak just in December 05'.

-Had some suspension work done this month (Jan 06') most likely not related.

There was a very light/almost indistinguishable tapping sound right after I got it back in Dec. from repair, but it didn't seem out of the ordinary.

Now, I am hearing a loud tapping (I am not calling it a knock because it does not sound like someone is hitting it with a hammer). The noise is prominent when sitting idle, and does increase in repetition with acceleration.

My first guess was a lifter, or valve? But upon reading other threads is it possible this is an exhaust issue?

I say this because I did hit a pretty big ice pocket/hole the other day which slammed me down. Possibly the tapping had been going on as loudly before, but I hadn't noticed it until after this. Could be wishful thinking.

-Checked oil, fluids immediately, level was good, was clean. Had it changed and added Slick 50 just to be safe. Noise/tapping did not decrease at all.

After oil change, service engine light came on next day, and maybe I am imaging it, but I could swear exhaust is coming in through the vents. I do not know the codes yet, need to take it in.

Anyone know what I am dealing with here, so I can be well advised before taking it in? I appreciate any input...Thanks, Carie

[OverBoardProject]

Exhaust is the last thing that people check, but I've been finding that it should be the first place to look.

If it's the exhaust it'll either be a leak right at the engine or the manifold might have a hole or crack in it.

If it isn't exhaust it'll be a lifter.

Good Luck

[Rmbodie]

If you are smelling exhaust thru the vents , you probably have an exhaust leak .This could be dangerous ,CO gas !!!! Since you say it was overheating , the manifold could be cracked or seperated from the engine block somewhere . The EGR valve may not be tight . Some things have to be retorqued after a reassembly. Rob

[lady_x_calibur]

Thanks for the help all...

It quit on me the other day, needed a fuel pump. Mechanic says knocking is a lifter, but not to worry about it !/? ha ha...

I am going to try to quiet the noise best I can by running synthetics through, etc...

If I cannot get it to quiet down, I will have to do the lifters because this noise will drive me bonkers. Mechanic says it will run approx. $400-$500.

Again, thanks all!!

[OverBoardProject]

Can you get us an audio clip of the motor running.

I just don't trust mechanics that say to not worrry about it.

[blazes9395]

It could be something as simple as a leaking exhaust at either where the manifold connects to the exhaust y-pipe, or at the exhaust manifold itself. I would bet on the first one, its common for an exhaust leak to start there and since you said to hit something, you probably dislodged it even more and created a bigger leak. You will get a tapping sound much like a lifter but it the exhaust valves closing. It would be like a clanking/tapping sound, usually(but not always) its louder when the engine is cold.