rattling under hood

[Toolman23]

I have a 2009 GMC Sierra with about 46k miles. when coming to a stop there is a rattling sound coming from either the passenger side under the dash board or under the hood. It only happens when slowing down and coming to a stop, and goes away once I accelerate and reach about 15-20 mph. Anyone have any ideas on what it may be caused by?

[Z71Steve]

Do you have an aftermarket CAI?

[Toolman23]

No, it's all stock.

[Lv1G6He3V2]

My '99 makes a similar sound. I was told it's the a/c compressor, not sure if it's normal or dying. I also have a rattle under my driver's side dash, but a lightweight dash cover made the noise stop. I hope you find it soon, these noises can be annoying.