Hello and thank you for trusting us with your question. I'm DJ.
If the radio only makes the hissing sound on AM or FM, the most likely cause is a disconnected antenna or a faulty antenna.
If the sound comes through even with a CD playing, then it's a problem with the tuner or the wiring to the tuner.
If the sound is related to engine speed, then it's likely to be a suppressor that's failing under the hood.
These are the most common causes of this. Rarely we find something else but that's about 2% of the time.
Is this something that you intend to fix yourself or will you be taking it to a shop that you trust?
I am getting a signal but also heavy hissing interference. CD is perfect.
How easy is it to get to the antenna to see fit is unplugged. And where is the antenna (rear windshield???)
How does the C pillar trim come off?. Do I put a screwdriver under the edge and ease it off...? Is it held on with poppers? I don't want to damage the trim.
The panel is trapped by the rear windowsill. I am afraid of pulling too hard. Are these poppers strong?
BTW the interference seems worse with the engine turned on.......