Weird noise from FHW boiler residential

customer sent me a strange noise from the boiler it sounded like an old man huffing and puffing i heard the noise when I got there, I let the boiler run for two min. on shut down it made it if boiler did not run long enough it did not make it customer said its loader on start up then goes away * started by cleaning the boiler oil filter, can nozzle check spark then tested pump of the carlin ez burner psi @ 120 psi did not fluctuate as I was thinking it was combustion test good, good draft.

Then started to test system on and off to fined the noise found it was on the water side between the top supply first 90* to the return boiler pis did not fluctuate noise is not air I know what that is
noise just started mo. ago customer said

one thing I was was expansion tank was teed 3" after it left the boiler this is where nose is and aura stats tank is new ApR 18 but was this way for 5 years yes I know its not right but its hard to get someone to pay for something thats been working. the pipe goes up 24" or so 90* then b& g main spiral vent to main header noise is mostly from here to return check all pump none make in noise.

When I get time I will post noise