The only time I've noticed a bit of off flavor similar to what you describe in my bottles is when I clean with oxyclean (or similar) and don't get a good rinse.
I now only use oxystuff to remove labels. When I finish a beer, I make sure it's rinsed well and at bottling time and I sanitize in the dishwasher. At the same time, I sanitize my bottling bucket with starsan and submerge the bottles that didn't fit in the dishwasher into the bucket for 5-10 minutes and drain on a sanitized bottle tree. No more off flavor.