Manifold or tappets?

[izthewiz]

My Chimp has had the precats removed according to the previous owner, and I've read somewhere that some side effects of this are noises that mimic those of tappets or a cracked/leaking manifold, which I can hear, but not identify.

Is there an easy/cheap way to ascertain the exact source of the noise?

I await the bestowal of the collective PH wisdom....

[Belle427]

I would say it does not mimic them to be honest but manifold gaskets are very common to fail.
A pita to do but maybe something to think about if just as a maintenance job.
Tricky to pin down, the old tissue paper trick may help holding it in various places to see if it blows around.

[TarquinMX5]

I can't say that I've heard that 'mimic' view before. Presumably no obvious marks on the manifold to indicate leaking exhaust gas?