Ok, that may indicate two or three things...read thru then decide...
Injectors, air intake, TBI / MAF sensor - these may be on plastic but wiring routes to snorkel and then to loom around the spark plugs - these sensors "adjust" as you drive - these need to be checked right down to the ground lugs on the engine block.
One Fan, one type of fan is in the engine compartment (Radiator or AC) - if it's ground lug to frame connection is bad, or the fan got whacked by road debris - replace it - because more than likely it got or has - water entry or the noise suppression in it has failed (seals have failed and the bearings are going out)
Another deals with the Passenger compartment fan - that is more of a deal breaker - especially if you have to locate the radio close to it. Because it may be from the fan, or the "damper" that handles air intake.
Heck for grins and giggles, I used to own an older Chevy Nova, 262 V8 Rochster2GC carb that had exhaust that smelled better than some of these newer (ahemn) POS - I would think not, but do you have turbo? How about a hood scoop? "Deconverted" back to stock? Did a bolt come loose from the mod? IT definitely seems to be engine related, just hope it's not an Air BAG sensor on a bumper somewhere letting you know in it's own particular way - that you have something ready to fall off. Or even your hood - ready to come off...
Gotta' do some diggin' into the floorboards. Hope yours is not like mine where I found rust and leaks that had standing water from all those years. Mine was two fold, the AC unit drain pipe that allows the condensate from the condenser unit to drain out - got plugged and water piled up and overflowed.
Long time ago I Bought a car used and should have taken more attention as to why I did not see water under the car when I used AC on hot days - biggest clue as to something is wrong.
Another was prior accident damages they don't tell you - had a grommet on the rear brake lights fail. It allowed all that salt, water snow and ice drain into the truck by the spare tire - a hard lesson learned there too - do like digging for a lug wrench and jack only to find them rusted onto the trucks bottom floor pan.
IF fans are not the noise, then it comes from the EVAP or antenna - you have something either in a panel close to that antenna (EVAP is close to the Gas tank - the valves at least) that is coming loose on Torque - when you accelerate decelerate - like a suspension part that if the grommet is letting the bolt strike metal - the noise from the road static can travel up into the frame making this type of noise.
The AM versus SSB reference means it a broad range of noise - this may be a ground loop issue within the radios own wiring to the vehicle. If your antenna and bracket are grounded / bolted to the frame, take and REMOVE the ground wire from the Radios' power wire - disconnect it, use the Radio Case ground or Coax shield for ground - if the noise abates - then the PROXIMITY of the ground wire grounding point and whatever the noise source is, is close by to its' connection point. (Again, back to engine - loose component due to torque or grounding wire is closer to noise source injection into ground of the frame.)
If you "borrow" a power feed - look for where it comes from. Some vehicles use a separate Frame to Battery and Engine To Battery ground scheme - which is for "detection" of power drains like cargo lamps, interior lights or even the running light head light system - can be switched off. In your case, you said you went straight to the battery. So I can only hope the routing there is as short and sweet as possible.
