Many audio amps use dual supply. A single 30 V supply is usually safe, though in principle can become dangerous when really wet.
It it's a dual +-30 V supply you should be more careful - that's about the legal limit from which on DC voltages are considered dangerous. So don't tough things on purpose, but not yet really dangerous - as long as you only touch one side.
There are solid state amps with higher voltages (e.g. +- 60 V) too, if this is high power.
The warning of the meter might come early, just in case, especially if it is AC voltage present at higher frequencies.