Wheezing sound behind dash on a '98 Blazer

I own a '98 Blazer.....when it starts up it has this very annoying wheezing sound behind the dash. The 'behind the dash' noise continues when it's in drive unless you throw the RPM's above 1500 or so at which time it stops completely.

I thought maybe it's something in the exhaust system....maybe back pressure and when the RPM's kick up it has enough pressure to free up whatever is causing the noise?

Any help would be great

1. Vac lines manifold to reservior can drivers side behind ABS rot out.
2. 4wd lines to actuator leak.
3. If vibrating noise PCV on throttle line - check that plastic holddown to the rear of intake still connected - after gasket done the connector is always broken. Also the PCV rubber sections.
4. If water noise, clogged heater core.
All change with rpm. Had them all at one time.

I would agree on the heater core being restricted. Backflush it and it should fix your problem.

Vacuum lines going to the heater controls is off or cracked.

Remove and check, a heater core does not weaze.

I have a similar noise sharing the same characteristics on my 96 blazer. I would describe my noise as more of a grinding/clicking noise. The sound goes away as you goose the throttle and seems to happen worst in colder temperatures. The crazy thing is that i've been replaced all the vacuum lines and concluded that the noise has to be coming from inside the dashboard - inside the car. This very noticable and rather annoying noise cannot be heard from the engine compartment. Noise has been there ever since i purchased the vehicle three years ago. Any suggestions??? Everything in the car in mechanically sound.

I have a similar noise sharing the same characteristics on my 96 blazer. I would describe my noise as more of a grinding/clicking noise. The sound goes away as you goose the throttle and seems to happen worst in colder temperatures. The crazy thing is that i've been replaced all the vacuum lines and concluded that the noise has to be coming from inside the dashboard - inside the car. This very noticable and rather annoying noise cannot be heard from the engine compartment. Noise has been there ever since i purchased the vehicle three years ago. Any suggestions??? Everything in the car in mechanically sound.

You'll need to start your own thread before someone can help you. This is curtishall's thread.

Sorry about that. Newbie mistake