Tone Rules

When I hear the pronunciation of the mandarin words I can hear that the tones are different than the pinyin. I can't seem to find a place that teaches me how the pronunciation of the tones changes despite what the pinyin says. Aren't there rules for this? For example, is it true that for ni hao they should both be 3rd tones but because there are two 3rd tones together the first word "ni" becomes a 2nd tone and the "hao" stays a 3rd tone? Thanks and let me know where I can find these rules.

Chinese does not like trying to pronounce consecutive low (3rd) tones. As a result, one of the 3rd tones becomes a rising (2nd) tone. Language and Culture lesson 1.7 does a good job of explaining this. If you have three consecutive third tones, the middle becomes a rising tone (wo hen hao). Likewise, if you have four consecutive low tones, every other (2nd and 4th) becomes rising (wo ye hen hao). There are a few other rules involving yi and bu but I don't remember them off the top of my head. http://members.rocketlanguages.com/lessons/285 One other rule - if you have consecutive 4th tones (falling), the second falling tone starts a slightly lower pitch than the first.