Tubed Pre Dying? ?

I've noticed that there is now some (faint) noise coming through my system where there was none before. Could this be a signal that my CJ tubed PV14L may be in need of new tubes? I bought it here, used, but the tubes shouldn't be more than 1.5 years old.

What are the signs of dying tubes?

Thanks for any suggestions.
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My friend has a PV14L, nice preamp. He is sending his to the factory for a mk II version upgrade, which I believe includes re-tubing. It is only costing him about $275 + shipping. There are other cap/resistor/? upgrades as well. This may be something for you to look into.

I just changed the tubes on my CJ PV14L today. It took me about 10 minutes. Order some tubes online. Try
You may want to contact CJ about retubing and if the unit
may need to be rebiased. If not you can get tubes online
and plug them in yourself.

If the unit is making a wooshing noise in the background
you may want to stop using it until you can retube, it
could be something in the power supply. Also look into
the cap/resistor upgrade mentioned by Jmcgrogan2, they
are probably part of the power supply stage, which may be
related to the noise.

Good luck,

Many thanks to all for the suggestions.