Hissy fit

I have a pair of Meridian 105 monoblocks and they both do this; a very low-level hissing noise from tweeters even with no pre-amp connected. Is this a sign of capacitors buying the farm?
How low of a level? How close to the speaker do you have to be to hear it?

ALL amplifiers produce some hiss/noise. If you have to move close to the speaker to hear it then I wouldn't worry about it.
I don't know if all amplifiers produce some hiss or noise, but certainly all systems I have heard do. My system produces a miniscule hiss- I have to remove the speaker grill and place my ear inside the exterior plane of the midrange driver to hear it. However, I never listen to music from that position!

This does not mean my system is better or worse than yours. Some are just quieter than others.

If noise is audible from your listening position, you should isolate the culpable component/cable/ or receptacle and repair.

Sean has written exhaustively on the method on this site.
I have to put my head up to the speakers to hear the hiss. Old amp, original caps.... just wondering....