Can water supply lines touch or rest on each other?
The only real issue is rattling noise due to vibration, or creaking due to thermal expansion. In this case, since one pipe is plastic, it's probably not a concern. I'd try to lighten the tension between them by flexing the plastic a bit, or place a rag between to act as a silencer. Be sure that by doing so you don't create a tight spot against the lumber, which can also cause noise.