rb25 weird sound?

Ok so i just finished rebuilding my motor and putting it back in the car. Well after getting it running i have noticed this weird noise. It started making this noise and after bout 2 days of starting it up and letting it run the noise went away and the car sounded normal. I then had the car sitting for bout 4 days and when went back out and started it up it started making this noise again. The best way i can explain the noise is it sounds like the exhaust is under water when revving up. Its like a weird bubbling noise. Ive checked the base timing twice now to make sure i had it set correctly and i do. IVe also adjust on the cas and still no change. Ive checked spark in all cyclinders. Motor compression readings were.160,165,160,165,160,170. If anyone has any idea or has had a similiar problem please let me know what you did to fix it or any suggestions to what i should try to fix it. If need be i can get a sound clip