I noticed a couple weeks ago that I was getting a drip under my kitchen sink. I didn't think much about it because I've always had a problem with the hose from the sprayer. Each time I used it, a few drops of water would travel down the hose from above. I kept a pan underneath, and it was dry most of the time. But this was different. I hadn't used the sprayer in a while. And the drip was getting worse. I finally decided to do something after one load in my dishwasher produced an inch of water in the pan.
Metal drain pipes disintegrate over time, from the inside out. Pinholes develop and the pipe starts leaking like a sieve.