My kitchen is pretty old. Fluorescent lights are built into (underneath) each of the metal cabinets.

Lately, and intermittently, I've noticed I get a shock when I either touch the counter beneath the cabinets or a cabinet door.

This was not happening when I bought the place and moved in 3 years ago.

Ultimately, I hope to gut and revamp the entire kitchen, but right now would be happy to get rid of the electric issue.

Can someone please tell me what the source of the problem might possibly be?

Most likely one the ballasts in one of the fluorescent fixtures is failing, ground faults from this type of fixture is common.

What this tells me is the fixture is not grounded properly, and now is energizing the metal cabinets.

Keep in mind, the other surface you are touching may be energized, and the fixture/cabinets may be grounded properly.

Best to shut off the breaker to these lights, or any other applaince that you have come in contact with, until you can get a qualifed electrician out to troubleshoot this issue.

While the shock you feel may not be enough to cause you harm, so far, one never knows if all conditions will be better the next time you touch this and receive a fatal shock.

Please get this looked at right away.

Another thought is a screw through metal cabinet into a live wire.
An Electrician should measure voltage with a meter(one probe to a known good ground or neutral, and other to metal cabinet, then turn off light, if power goes out to meter with light, it is likely a Ballast, as TK mentioned, and may need to disconnect each ballast until voltage is gone to identify which fixture.
If you turn off lights and it is still hot, they will probably remove Cabinet screws one at a time to locate problem and location of wire to repair.