I have a '97 Civic with 200k miles. The past couple months, I started to notice a new noise (other than the loose heat plate).

When letting off the accelerator at high speeds (60-85mph) I hear a noise that sounds like pressure releasing from somewhere. Along with the noise, the gas pedal falls a bit as well.

My fuel economy has gotten worse since the new noise started as well (down to ~26 from ~35). Not sure if these may be tied together or not.

Any suggestions on what to check first and/or where the noise might be coming from?

 

check for cracked or loose vacuum hose to start