Nmap shows strange open ports

Running nmap on my localhost shows me strange open ports:

$ nmap -p- localhost
Starting Nmap 6.47 ( http://nmap.org ) at 2015-12-28 12:14 CET
Nmap scan report for localhost (127.0.0.1)
Host is up (0.00047s latency).
All 65535 scanned ports on localhost (127.0.0.1) are closed

Nmap done: 1 IP address (1 host up) scanned in 2.51 seconds

$ nmap -p- localhost
Starting Nmap 6.47 ( http://nmap.org ) at 2015-12-28 12:14 CET
Nmap scan report for localhost (127.0.0.1)
Host is up (0.00046s latency).
Not shown: 65533 closed ports
PORT      STATE SERVICE
36642/tcp open  unknown
50826/tcp open  unknown

Nmap done: 1 IP address (1 host up) scanned in 2.55 seconds

$ nmap -p- localhost
Starting Nmap 6.47 ( http://nmap.org ) at 2015-12-28 12:14 CET
Nmap scan report for localhost (127.0.0.1)
Host is up (0.00050s latency).
Not shown: 65531 closed ports
PORT      STATE SERVICE
37700/tcp open  unknown
46694/tcp open  unknown
48334/tcp open  unknown
53438/tcp open  unknown

Nmap done: 1 IP address (1 host up) scanned in 2.60 seconds

$ nmap -p- localhost
Starting Nmap 6.47 ( http://nmap.org ) at 2015-12-28 12:14 CET
Nmap scan report for localhost (127.0.0.1)
Host is up (0.00046s latency).
All 65535 scanned ports on localhost (127.0.0.1) are closed

Nmap done: 1 IP address (1 host up) scanned in 2.51 second

As this ouput shows, the open ports seem to change fast and randomly. I cannot see these ports via netstat if I am interpreting the output the right way:

$ sudo netstat -tulpen
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       User       Inode       PID/Program name
tcp        0      0 127.0.1.1:53            0.0.0.0:*               LISTEN      0          17081       809/dnsmasq     
udp        0      0 0.0.0.0:5449            0.0.0.0:*                           0          30885       2855/dhclient   
udp        0      0 127.0.1.1:53            0.0.0.0:*                           0          17080       809/dnsmasq     
udp        0      0 0.0.0.0:68              0.0.0.0:*                           0          30321       2855/dhclient   
udp        0      0 0.0.0.0:45170           0.0.0.0:*                           107        15289       606/avahi-daemon: r
udp        0      0 0.0.0.0:631             0.0.0.0:*                           0          15931       636/cups-browsed
udp        0      0 0.0.0.0:5353            0.0.0.0:*                           107        15287       606/avahi-daemon: r
udp6       0      0 :::34146                :::*                                107        15290       606/avahi-daemon: r
udp6       0      0 :::55654                :::*                                0          30886       2855/dhclient   
udp6       0      0 :::5353                 :::*                                107        15288       606/avahi-daemon: r

I tried to use lsof to investige these ports, but there is no result, I guess when nmap returns, the port is not open any longer:

lsof -i :`nmap -p- localhost|grep '/tcp'|cut -d'/' -f1|head -n1`

What can I do to further investigate this issue? Do I have to be worried? Is this normal? Should I suspect any malicious processes running?

Note that this Q&A is different as I am running everything on my local machine.