Very much so. AM interference comes from all over the place, including flourescent and neon lighting, any number of electric motors, electric fences, medical equipment, bad bearings (metal on metal contact), and most commonly, 1:1 scale cars. These problems with AM do not even consider the incredible lack of range compared to FM.
However, that's not to say that the FM spectrum doesn't experience interference.
DSM on the other hand, because of its incredibly narrow band [comparatively speaking], and the fact that this band exists higher than the 300MHz and below interference band, has VERY LITTLE chance o0f interference.
Bottomline, you get what you pay for. You will encounter interference on ALL bands, but your likelihood of such an occurrence decreases with the increase of the price.
With that said, I have done just fine with my FM 75MHz MX3 radio in ALL of my models. I have yet to glitch, and I just carry a bunch of crystals with me so I can hop over if someone only has one set and it just happens to be the one Im using.
Hope this helps, but I would DEFINITELY recommend upgrading your radio system. One of the first things I do when I get a new RC is buy a MX3 compatible receiver for it and get rid of the old system. ‡