Whistle Sound When Accelerating

For some time I've noticed a whistling sound coming from my 96 SR5 when I'm accelerating. It sounds like a turbo is kicking in but is not real loud. When the sound is bouncing off of the concrete wall of an entrance ramp, it is very noticable. It's difficult for me to tell where it's coming from exactly but seems to not be coming from the engine. Has anyone else heard of this issue?

 

Probably just girls whistling at your sweet 4Runner.

But, seriously, I've noticed a similar noise in my TC under medium acceleration. I wonder if it could be something in the intake tubing.

 

HA HA... yeah, I never thought of that..

 

I was wondering if it was a vacuum leak but I couldn't see any sources of hoses back there. I'm leaning towards a pinhole in the muffler.

 

Sounds like your supercharger