Well I just pulled the heads and man was this engine clean, I was expecting some sludge or build up after 135000 miles (2004) but there was really nothing. I don't know where the noise is coming from after all as the liners are 100% exactly where they should be with zero evidence of the headgasket being tapped, piston steam cleaned or anything, they are so perfectly level that you can't even tell where they and the block meet. Now I am wondering about lifters and wondering if it would be a good idea to change them as I am in there already. Sorry I was no help after all.

I did find that the back head bolts seemed to be much looser than the others (maybe why the headgaskets failed back there)? I can see where the dexcool had eaten into them a little as well.

 

I changed from dexcool to Prestone several years ago and have not regretted it.

Did it sound like it was coming from the middle of the engine or was it louder on one side than the other? With the frequency of the tap it is something weird like a cracked flex plate or something that relates to one cylinder/piston/valve set.

 

I was adding coolant pretty regularly...
Then I did what everyone says not to do: add a leak stop product.
It worked. I haven't had to add coolant since.
The tap was there long before, and long after, so it's not a coolant issue for me.

I'm wondering about the oil pressure or a failing cooling fan, as others have mentioned. Haven't had time to check either yet, but those are the two on the list.

 

A cheap way to raise your oil pressure is to put on a bigger filter. The wix 51459 is about twice as big as the stock size.

The coolant passages from the block to the heads are in the back so loose bolts back there would be an issue, for sure.

 

I know mine isn't the cooling fan as I converted to GM HD fan clutch and older full ring fan and it made no difference on the noise. Also I am not sure about the oil pressure in mine as it does it cold as well. I went ahead and ordered all new lifters as I am already in there and it will take minutes to replace at this point. I am taking the heads to the machine shop to get checked out and then put everything back together. If no change I will probably plumb an oil pressure gauge to check that. There is always motor honey lol.

 

I have the same sound but more persistent at acceleration! Just spent the weekend changing the oil pump and timing chain/sprockets. The pump was split and all signs pointed to that but the sound is still there!! Had a head rebuild last year as well May be I should play this game as well!!
Any suscess finding it?

 

So what's the final verdict jwigum? what is/was the tapping/ticking noise, I'mm sitting here with bated (spelt either way, bated or baited) breath wondering

 

Had the exact same sound earlier this year. Turned out to be the Y pipe to muffler connection. Sounded completely mechanical, and varied by RPM. Y Pipe was rattling at the muffler connection. Replaced the rusted out bolts, tightened up the entire exhaust, noise was completely gone.

 

Finally had time to get mine back together and here is what I found so far and what I replaced. Replaced all the top end gaskets (incl HG of course), plugs and wires and lifters. I had the heads rebuilt at engine shop, they did mill them very slightly but said they weren't overly bad (can't remember how much). He said my intake valves were a little tight but everything cleaned up well. Put everything back together and started her up and the new lifters were loud for a few seconds and then quieted right up. I only had time to drive it about 10 miles and everything seems quiet so far. If it stays quiet I am leaning to a weak lifter but who knows.

 

So it must have been a lifter?