I have a 1998 S70 GLT 137K miles with a strange noise. The noise sounds like a pump making a "put-put-put" kind of sound and is most audible coming from the front fenders (about equal volume on the left and right side of the car). The speed of the "put-put" changes--it starts slow and then jumps to a faster "put-put". I've monitored it for some time and the sound seems to start when the radiator fan turns off, and then stops once the radiator fan kicks on again.

I'm battling a P0455 CEL code as well. I replaced the gas cap with an OEM cap today and reset the codes to rule out the easy solution. Can these issues be related in any way?

 

Yes it may very well be connected.
You might be hearing the Evap valve running.

Look under the hood there is a Valve mounted to the radiator fan.
It has 2 hoses going to it and an electronic connection.
Follow the hose from the valve to under the car. Check good for holes.
The hose is known to fall from time to time and when people hit the parking stops it will cut the hose.

 

If I find a hole in the vacuum hose, what is the best way to get a replacement? Is this hose commonly available at auto parts stores, or is it specific to this vehicle for this part?

Thanks for the help!

 

Depends on where the holes is.
There is hard plastic hose most of the way. If there is a hole in the plastic hose then cut the hole piece out and reconnect with a piece of regular vaccum hose.

There might be a hole in the rubber line somewhere else. Which you can get from pretty much any auto parts store.