HooRU Many stevia mixes add things to it such as erythritol (a natural sugar alcohol which has been linked in recent studies to cardiac issues). Look for a brand that doesn’t include extra stuff. Another thing is that because of the concentration stevia and water mixes will crystalize over time leading to a white precipitate but putting the bottle in warm water will dissolve them making it a clear solution again.
Stevia is way too sweet and yes the profile is not quite the same as sugar but compared to other natural and synthetic ones I think it comes closest to sugar, however the obscene amounts of sweetness in drink (such as Coke) are very hard to do with any sweetener other than HFCS/sugar, but that is ok because 39g of the stuff in a 12 fl oz. can is batshit insane. This political orgy of putting real sugar back into products loaded with sugar heavy products is just stupid. But here we are out of the Age of Aquarius and into the Age of Arrogant stupidity and many other things. Never cared for aspartame, it seems almost metallic in taste with an aftertaste, I would sooner drink water over a diet soda but again those products use so much of the crap its a poor comparison of the product when used at lower levels.
The thump thing could be caused by a skipped beat (PVC - pre ventricular contraction), it happens but you might want to talk to your doctor about it if you can to rule out any other issues.
As for the lead in pipes some areas offer financial help to have them replaced with other materials, so long as your water board doesn’t screw up with the pH of the water most of the lead oxides will remain stuck in the pipe but honestly for the sake of the taste of chlorination, something with a carbon filter will improve the taste and smell of your water.