New 1/4in plumbing shakes when cold water shuts off; worried?
You probably have always had the problem but adding the T made the problem noticeable. As far as I see this there are 2 problems. First the plumbing is loose and needs to be secured you may have not heard it in the past but it was there adding the T may save your plumbing because now you know it needs to be anchored. 2nd be prepared to replace the saddle valve these things are trouble waiting to spring a leak at the worst possible time according to Murphy's law. Do you need to lower the pressure NO! Pipe movement is a flow issue pressure can make it worse but why sacrifice wonderful water pressure when all that is needed is to anchor the pipe.