I have couple of problems with my octavia 1.8t 20v '99.

FIRST: After 130 km/h my steering wheel starts to shake (only when i press gas paddle) when i release it, it calms down.

SECOND: I hear strange short noise, when i start driving (at about 20-25km/h). It only happens when i previously shift into revers then in first gear.

Does somobody know what could couse these problems?

FIRST - most likely your tracking is out

Second - If the noise only occurs when you reverse out of a space then drive off, and not if you reverse into a space, suspect the rear calipers or anti-rattle spacers in them.

If vice versa, suspect the handbrake linkage.