I have a strange situation with a whining noise that I believe is coming from my water lines. The noise is very hard to trace, but I believe it occurs AFTER running hot water (shower, faucett, etc.) The noise can be stopped by running either hot or cold water - it may stop for only a short time and then return. The noise only occurs for about 20 - 30 minutes, not continuously, and only after running hot water. Any thoughts on possible causes?