From Der Speigel on line -
Should you end up living in Germany, however, knowing how to deal with the neighbors is vitally important. The following is a brief list of the ordinances and rules you need to know:
QUIET TIME (Ruhezeit): Quiet time is from 8 p.m. until 7 a.m. and all day Sundays and holidays. A little quiet snoring is allowed, but house and garden appliances and machinery are off limits. No midnight clothes washing or Sunday afternoon lawn mowing.
The southern German state of Hesse used to have a legally mandated quiet time from 1 to 3 p.m. every afternoon. It was repealed last year, but many will still ask you to keep it down during this time. You are, of course, fully within your rights to ignore such requests after all, the law is on your side should you want to practice drums in the garden after lunch but keep in mind that you have to live with these people.
If you have any specific questions, like: Can I use my brand new Super X-G ACME chainsaw to trim daisies on sunny summer afternoons?, ask the Ordnungsamt representative (usually located in your local city hall).
WASHING YOUR CAR: Generally not allowed because of the chemicals in the soap seep into the ground water. Still, you can get away with it (use dish soap) as long as none of your neighbors complain.
BARBEQUES: The general rule is that you're only allowed to grill once a month. Of course many of us grill much more often in the summer months. What's important is that the smoke and smell does not bother your neighbours. If you live in close quarters, perhaps just let your neighbours know when you're firing up the grill so they can close the windows, or move your grill to the other side of the garden.
PARTIES: Generally you are allowed to make noise outside until 10 p.m. Again, it may not be 'excessive'. The 'rubber-rulebook' also says you may have bigger parties up to four times a year. If you're planning a major bash, perhaps it would be a good idea to tell the neighbours ahead of time, or better yet, invite them too.