Ken,

You'd be better off using an antenna just to check for radiated noise as well
as conducted noise. You'll have to tune across each band because the hash
might be frequency specific and/or broad band. Depending on a lot of factors,
it can sound like a buzz, hum, variations due to load, etc. but if it's there,
it will be easily recognizable as a "non-signal".

73s,

Evan