Why I cannot hear clear sound from simple GNURadio block - gnuradio

Question

I made simple FM Radio in GNU Radio but I cannot hear clear sound. It just makes very noisy, chopped sound. Even dial-tone example makes same problem.
Is there anyone who met same problem??
My environment:
VM in Virtual box(2 core, 1GB memory)
ubuntu 14.04.4 LTS
GNU Radio 3.7.9
Dial-tone example(same with original one in official website..)
#!/usr/bin/env python
#
# Copyright 2004,2005,2007 Free Software Foundation, Inc.
#
# This file is part of GNU Radio
#
# GNU Radio is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3, or (at your option)
# any later version.
#
# GNU Radio is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with GNU Radio; see the file COPYING. If not, write to
# the Free Software Foundation, Inc., 51 Franklin Street,
# Boston, MA 02110-1301, USA.
#
from gnuradio import gr
from gnuradio import analog
from gnuradio import audio
from gnuradio.eng_option import eng_option
from optparse import OptionParser
class my_top_block(gr.top_block):
def __init__(self):
gr.top_block.__init__(self)
parser = OptionParser(option_class=eng_option)
parser.add_option("-O", "--audio-output", type="string", default="",
help="pcm output device name. E.g., hw:0,0 or /dev/dsp")
parser.add_option("-r", "--sample-rate", type="eng_float", default=48000,
help="set sample rate to RATE (48000)")
(options, args) = parser.parse_args ()
if len(args) != 0:
parser.print_help()
raise SystemExit, 1
sample_rate = int(options.sample_rate)
ampl = 1
src0 = analog.sig_source_f (sample_rate, analog.GR_SIN_WAVE, 350, ampl)
src1 = analog.sig_source_f (sample_rate, analog.GR_SIN_WAVE, 440, ampl)
dst = audio.sink (sample_rate, options.audio_output)
self.connect (src0, (dst, 0))
self.connect (src1, (dst, 1))
if __name__ == '__main__':
try:
my_top_block().run()
except KeyboardInterrupt:
pass

Answer 1

This example works very well on my machines.
The noisy common reason for problems like these is the fact that virtualized sound cards don't work quite like their real counterparts, especially when the virtualizer tries to resample
I'd bet your problems go away as soon as you run your GNU Radio natively, instead of in a VM.