I bought a 2-hand opel astra g bertone ... engine not in a good shape so the rings, clutch and oil pump had to be changed. The engine is quiet but when over 3000rpm its way too loud, and the noise comes from the passengers (right) seat. The noise can be described like low frequency bass engine sound.

If the revs go under 3000rpm i can hear only wind.

can it be a noise reduction material missing or cracked ...??