as mentioned above, its charcoal canister, part of EVAP, u might be hearing purge valvue operating right after driving car for a min.
Im not sure if 2NZ FE is equiped with this or not but its there in 1ZZ FE variants.
1NZ FE is 1500cc as compared to 1300cc 2 NZFE
please check and confirm the engine number from the excise document to know whether the engine is swapped or not.
Other guess is that only the intake manifold is swapped with 1NZFE, as the internal galleries get damaged and produce a weired sound after a certain period of time.
the Potentiometer attached to right shock piller is to adjust the AFR of car, better dont fiddle with it if its set at factory position.