Those things which render the Salaah invalid

Making sounds in Salaah

Q: While reading namaaz different types of sounds come out like when I close my lips and while opening the lips and due to the movement of the tongue some sound is generated and while reading rabbana lakal hamd near hamd different sounds comes out, when the tongue touches the upper lip. Do this kind of sounds invalidate my salaah? Can you tell me which kinds of sounds invalidate salaah and which of them don't?

Turning in Salaah

Q:

1) In salaah, if you move your head in any direction (right, left, up, down, back or forth), does this nullify the salaah?

2) Moving your chest in salaat in a direction away from the qiblah, does this nullify salaah?

3) If your pants has a small hole and your skin is visible through the hole, performing salaah in this state, will your salaah be valid?

4) If the underneath of a shoe touches the top of your feet, do you have to wash that part of your feet before performing salaah?

Saying Aameen in one's heart in Salaah

Q: As far as I am aware, speaking intentionally or unintentionally will nullify the salaah and it will have to be re-prayed again according to the hanafi maddhab (although, if I am incorrect in my understanding then please correct me jazak Allah khayr). The question I would like to ask is that say for example, if I recite اَللَّهُمَّ رَ‌بَّنَا آتِنَا فِي الدُّنْيَا حَسَنَةً وَفِي الْآخِرَ‌ةِ حَسَنَةً وَقِنَا عَذَابَ النَّارِ‌ and in my heart I say Aameen but my tongue may move slightly unintentionally, however there is no sound of any letters coming out, can that be classed as speaking in Salaah?