The exhaust system must be comparable to that designed for that specific vehicle as standard factory equipment. It must be in good working order and in constant operation to prevent excessive or unusual noise.
Yes, an Officer can follow you as long as he/she wants, but when they say something such as "I've been looking for you", then it gives the appearance that the Officer has some preconceived feeling or that the encounter will be on a personal level.
Anyway, until you comply with the law, you stand the chance of getting pulled over again. Or as some people say, "harrassed". It never ceases to amaze me that when people get caught for breaking the law, i.e. not having both tags properly affixed to the vehicle or for not wearing a seat belt, they want to vent about it. If we would learn and comply with out local laws on small matters like objects dangling from the mirror, a charcoal cover on the license tags, stickers on window obstructing view, then the Police would not have an opportunity to pull us over. But, then again, most people like the Police attention.