NE555 speaker voltage spikes
The speaker has inductance  and so does any power supply rail .Bypass the supply rail at pin 1 and pin 8 of the IC with a electrolytic of say 1000 microfarad .Remember that tha 555 output stage takes power spikes due to crowbarring ,This is stated in the www.badbeetles.com   website .The 555 isnt designed for 8 ohm in fact the output current capability depends greatly on the manufacturer.Placing 47 ohm in series with speaker will help but reduces available volts for speaker.If you want anything like full output voltage swing then use a complementry emmiter follower after the 47 ohm and before the cap . Your 10 microfarad cap should be inreased in value because i am assuming it is electrolytic .Reasoning is ripple current so go for 470 microfarad which is a very typical audio output coupling cap value .The electro will last a long time ...