my volvo s40 2004 is making rattling noise when i step on the gas anything ideas ?

Check your heat shields that run all along your exhaust pipes. They usually come apart.

okay i will take it to the shop and let them check it today i hope thts the cause. bcos i already change the belt tensioner and the noise still there whn i only step on the gas

Loose belts or bad pulleys usually squeal when they get bad or dried out. A rattle is related more to a loose part like a heat shield. Have you been using a different gas lately? The rattle you think you hear may be a spark knock.

I was using a regular gas n later I found out it use only premium so I let the old one runs out n I filled it wit premium.

That's probably your rattle then.

I took it to the shop they said there is something loose are the timing cover or a part going bad . It was a replace engine tho forgot to mention tht