I would try the RO water. I suggested the campden tablets a few posts earlier and they help but since then I have used RO and I think it tastes cleaner. Just try to find a water machine and fill a carboy or two. Should be about 30 cents a gallon.
I will be trying the RO water for next brew.
What's interesting is that I tasted one of the IPA's brewed by a local brewery and I picked up a hint of the same off flavor that I've been tasting in my IPA's.
I spoke to their head Brewer and he told me that they use untreated tap water, run through a filter.
This is in S Florida.