No. There is no special requirement for a "Subwoofer" cable. Subwoofer signals are so-low frequency and such a narrow band that nearly any coax-based cable with RCA plugs will do.
(as you get into higher and higher frequency like video and digital - different story)
My subwoofer was running with a 25' of white CATV coax and "F-to-RCA-Male" adaptors for months and it sounded great.
Subwoofers do seem to prefer a tight-fitting RCA plug. This is one thing you do get with a name-brand (Monster) subwoofer cable. But many inexpensive cables work great (AR Pro series, Radio Shack, GE).
When you say regular coax cable...do you mean RCA jacks? or coax...such as used for Dolby Digital connections? My sub humms even when not in use..and I've reied using other power strips..but it still humms. Any ideas?
The "regular coax" ends you are refering to are actually called "F" connectors. You can get gold plated F to RCA convertors at radio shack for about $2.99 each. Very good quality quad shielded RG6 actually makes an excellent subwoofer cable. It has very little signal loss over a long run and can easily be converted from F connectors using the adapters described above. If you want to invest in the tools, which are not cheap, you can actually terminated the coax directly with RCA connectors rather than F connectors. Do a search on Canare in this news group for more details.
2. is your subwoofer using an external amp hence connected via speaker wire or is it using an internal amp connected via an RCA cable? It sounds like it has an internal amp?
3. does your connection between your sub and receiver run parallel to (close) or on top of a power cable for any reasonable distance?
4. do your other speakers emit a similar hum when connected?
5. do you have any possible sources of interference near the system i.e. flourescent lights, motors, etc?
6. Do you have cable TV running into the house? Is it connected to something (like a cable box or VCR) that is then connected to your receiver/preamp? Does the sub stop humming if you unplug the cable TV connection (the one coming from the wall) from the cablebox/vcr?