Just installed a new Delta kitchen faucet. Installed without a problem however when hot or cold water is on at a low flow the faucet supply lines under the sink whistle. The whistle varies with the flow and then dissapears at full on. The new Delta faucett supply lines are plastic and replaced the original rigid copper lines to the old faucet. the pitch of the whisle also changes when supply lines are moved with water running throught them. The house is 2 years old and the plumbing is PVC. Any idea of what could be causing the whistle? There were no noises prior to the new installation and the kitchen faucet is the only faucet making noise. Any help would be appreciated.