2000 Explorer. Rattle noise at high speed

My ford explorer sport 2000 (manual transmission) with 60000 miles has had a noise for about 4 months. It is like a rattle but not to loud. It happens in different situations. When I am the highway and accelerate very hard with one pedal-push (at high speed only), it makes this noise while accelerating for a few seconds until I reach the desired speed. When the car reaches 65-70 mph or more and I keep it on 70 mph or higher, it maintains this noise solid until I reduce to less than 70 mph. I had another truck long time ago with the same problem. Someone told me it was the oil I was using (too heavy). I never had the chance to check if that was the problem ‘cause I lost it in a crash. Now, I use Castrol full synthetic 10-30 and I have the same problem. I was using Castrol full synthetic 5-30 before but when the car was without acceleration at all (on neutral) I had a noise I did not like (like the valves). I really do not know what to do about the oil and I have to change it very soon. Could someone give me an advice? Perhaps it’s not the oil...